Fluid catalytic cracking (FCC) is primarily used to convert high boiling, high molecular weight hydrocarbons from petroleum into lower boiling, lower molecular weight compounds. The lower molecular weight compounds include gasoline, olefinic compounds, liquid petroleum gas (LPG), diesel fuel, etc., where the feedstock and the operating conditions can be adjusted to improve yields of a desired product. Hydrocarbons are cracked with a catalyst in a riser in an FCC unit, coke deposits on the catalyst in the riser, and the coke is burned in a regenerator to regenerate the catalyst. The catalyst is repeatedly cycled through the riser and regenerator while cracking hydrocarbons.
There is high demand for diesel fuel, and there is also a high desire to use renewable feedstocks for fuel. The FCC unit can convert some petroleum feedstocks into diesel fuel, such as vacuum gas oil, but the resulting diesel fuel often has a low cetane number. Renewable feedstocks, such as natural oils that include triglycerides and/or fatty acids, can also be converted into diesel fuel in an FCC unit, and the resulting diesel fuel often has a high cetane number. Vegetable oil is a renewable feedstock, but the supply of vegetable oil is limited so the amount of fuel that can be produced from vegetable oil is also limited. Diesel fuel from vacuum gas oil can be combined with diesel fuel from vegetable oil to produce a product with an acceptable cetane number for use as diesel fuel, and the resulting diesel fuel is partially produced from a renewable feedstock. However, vegetable oil needs to be processed in the FCC unit at a lower severity than vacuum gas oil or similar feedstocks to maximize the production of diesel fuel, so co-processing vegetable oil and vacuum gas oil results in reduced yields over separate processing. It is difficult to economically justify dedicating an FCC unit to processing vegetable oil because of the limited supply, and sequential processing may require additional storage facilities, reduced output for downtime between different feedstocks, and a more complicated production schedule. However, due to environmental impacts and regulations, refiners may want to process a certain amount of feedstocks that are allocated to renewable resources.
Accordingly, it is desirable to develop methods and apparatuses for co-processing vegetable oil and petroleum based feedstocks in an FCC unit. In addition, it is desirable to develop methods and apparatuses for co-processing vegetable oil and petroleum based feedstocks in an FCC unit where the vegetable oil is processed at a lower severity than the petroleum based feedstock. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawing and this background.